1. Field of the Invention
This invention relates to a printing head having a plurality of recording elements (e.g., in ink-jet nozzles, heating elements, wires, etc.), ink jet cartridge, and to a printing apparatus employing such a printing head.
2. Description of the Related Art
A printing apparatus using an ink-jet printing head has become the focus of much interest not only because the noise produced at the time of printing is so small as to be negligible but also because of the high printing speed and the ability to print on plain paper. Among such printing methods available, an ink-jet printing method described in Japanese Patent Application Laid-Open (KOKAI) No. 54-51837 and German Patent Application Laid-Open (Dols) No. 2843064 differs from the others in that thermal energy is made to act upon ink to obtain a motive force for discharging a drop of the ink. More specifically, the printing method disclosed in these publications produces a change in state accompanying a sudden increase in the volume of ink acted upon by thermal energy, and discharges the ink from an orifice at the tip of a printing head by a working force based upon the change in state, thereby forming a jetted drop of ink. The ink drop attaches itself to a printing medium to perform printing.
The ink-jet printing method described in German Patent Application Laid-Open (Dols) No. 2843064 not only is effectively applicable to a so-called drop-on-demand printing method but, since it is of the full-line type, the method also readily lends itself to a printing head in which multiple orifices are provided in high density. Using such a printing head makes it possible to obtain a high-resolution, high-quality image at high speed.
The printing head of the apparatus applied to this method comprises an ink discharge section and an element base board. The ink discharge section has orifices provided so as to discharge the ink, and ink passageways communicating with the orifices and having a heat applying section for subjecting the ink to thermal energy in order to discharge the ink. The element base board has electrothermal transducers (heating elements) which generate thermal energy.
By virtue of technological advances made in recent years, the base board is no longer merely composed of a plurality of heating elements on a substrate. Now a driver for driving the individual heating elements, a shift register for holding serially entered image data, converting the data to parallel data and outputting the data, and a latch circuit for temporarily storing the data outputted by the shift register can all be constructed on the same element base board.
FIG. 5 shows an example of the circuitry of the base board constructing the conventional printing head. Specifically, FIG. 5 illustrates an element base board 600, heating elements 601, power transistors 602 constructing a driver circuit, a latch circuit 603, a shift register 604 and input pads 605 611, namely a pad 605 for inputting a clock signal, which is a synchronizing signal for image data that enters from pad 606, a pad 607 for entering a latch signal, a pad 608 for entering a drive pulse (strobe signal) to externally control the ON time of the power transistors 602, namely the time during which current is passed through the heating elements 601 to drive them, a pad 609 connected to a power supply (5 V) for driving logic circuits, a pad 610 for ground (GND) and a pad 611 connected to a power supply for driving the heating elements.
According to the driving sequence of the printing head having this construction, first image data from the printing apparatus proper is synchronized to the clock and outputted to the element base board 600 serially. This image data is held in the shift register 604 and is temporarily stored in the latch circuit 603 in sync with the latch signal. As a result, ON, OFF outputs conforming to the image data are latched. When heating pulses are applied under these conditions, a power transistor which corresponds to ON ("1") image data in the latch circuit 603 is turned on for the duration of the high-level heat pulse and a current flows into the heating Element 601 connected to this power transistor, whereby the heating element is driven to produce heat.
Further, the ink-jet printing head is attached and detached by the user for reasons such as replacement of an ink cartridge. If the printing head is not attached properly and the electrical contact between the ink-jet head and printing apparatus proper is insufficient as a result, the printing head may be driven abnormally and may even be destroyed. Accordingly, it is designed for signal Lines inputted to and outputted from the element base board to be provided with pull-up or pull-down resistors in order to avoid these problems.
As described above, logic circuits such as the shift register 604, heating elements and the power transistors 602 are formed on the element base board 600. However, a problem encountered is that when a plurality of the heating elements 601 are driven simultaneously, a sudden fluctuation in current occurs and happens to cause a fluctuation in the voltage of the clock and the generation of noise, as a result of which the logic circuits provided on the element base board malfunction.